The present invention relates to a novel and useful data collection system.
In the prior art, a data logger normally works in conjunction with a programmer/down-loader personal computer, or a data collection instrument of some nature. The prior art systems use a conventional RS-232 serial data communication system which is a restrictive format. A data logger operating under the RS-232 serial format utilizes two lines, transmit (Tx) and receive (Rx). For example, when a personal computer communicates with the logger in the prior systems, the RS-232 protocol must be followed. In addition, data transmitted over the Tx and Rx lines utilize a fixed time interval for the rate of transmission, measured in bits per second. The standard rates under the RS-232 system begin at a standard of 2,400 bits per second and double for increasing data rates. For example, typical rate steps are 2,400, 4,800, and 9,600 bits per second. When logging environmental logging environmental parameters, logger products tend to use a maximum of 9,600 bits per second. In other words, 18 bit data word per millisecond or 1,000 data bytes per second would constitute the maximum rate of transmission under the RS-232 operation for a data logger. A deviation from these standard rate steps is not acceptable.
Moreover, a logger microprocessor utilizing the RS-232 data logging standard must include software procedures in a program memory (ROM) to handle the Tx and Rx lines. In addition, the logger microprocessor must generate the time critical intervals of the data rate. The received instructions or data from the host PC must be processed by the logger and stored in non-volatile memory devices, such as EEPROMS, to configure the operation of the data logger. At this time, the data logger microprocessor suspends all other operations when communicating with a PC. In other words, common terminal routines for the host PC exist to transmit and receive data from the RS-232 logger device. It should be noted that loggers of this type are supplied with the software programmed specifically to simplify data viewing and provide graphing functions by the manufacturers of such loggers.
Although the RS-232 serial data communication system works satisfactorily in certain cases, there are certain deficiencies which limit its specific application to data logger devices. As prior stated, the transfer of data takes place at a relatively low speed compared to the ability of a PC, which is capable of transferring data at 10 to 40 times the rate of an RS-232 device. Also, the logger unit must supply the power for transfer of data, which tends to limit battery life in self contained logging units. Further, there is a need to generate software which supports the RS-232 signal. This software "overhead" takes precious space in the memory portion of a data logger and it severely limits the capacity of the data logger to gather environmental values. In addition, the cost of the hardware necessary to generate an RS-232 format is relatively high. Moreover, data is not necessarily secure in an RS-232 system, since it is readily accessible unless safeguards are programmed into the software.
U.S. Pat. No. 4,689,740 describes a computer system which utilizes a clock bus wire and a data bus wire to transmit data. The object of the subject patent is to enable a single two wire line to be used for the interconnection of multiple stations.
Other two wire systems known as MICROWIRE (National Semiconductor) and S.P.I. (Motorola), are also adaptable to data logging operations.
A data transmission system which is particularly applicable to a data logging device without the use of an RS-232 serial format would be a notable advance in the instrumentation field.